\begin{tikzpicture}
    \tkzDefPoints{0/0/B, 1/0/C, 2.4/2/A}
    \tkzDefLine[altitude](B,A,C)  \tkzGetPoint{D}
    \tkzDefLine[altitude](C,B,A)  \tkzGetPoint{E}
    \tkzDefLine[altitude](A,C,B)  \tkzGetPoint{F}

    \tkzDrawPolygon(A,B,C)
    \tkzDrawSegments(A,D  B,E  C,F)
    \tkzDrawSegments[dashed](C,D  C,E)
    \tkzMarkRightAngle[size=0.15](A,D,C)
    \tkzMarkRightAngle[size=0.15](B,E,A)
    \tkzMarkRightAngle[size=0.15](C,F,B)
    \tkzLabelPoints[above](A)
    \tkzLabelPoints[left](B,F)
    \tkzLabelPoints[below, xshift=0.5em](C)
    \tkzLabelPoints[below](D,E)
\end{tikzpicture}

